1) Field of the Invention
The present invention relates to a method for fixing toxic or nontoxic waste material by allowing the waste material to absorb on an organic absorbent and mixing the waste material-containing absorbent thus obtained with a hydraulic binder and a hardening activator to form a hard material.
2) Description of the Prior Art
A method of this type is disclosed in Netherlands Patent Application No. 8901240.
According to this known method, organic waste is allowed to absorb into a modified variety of clay and the product obtained is mixed with Portland cement and fly ash to form a hard end product which has the characteristics of hardened concrete.
Although this known method gives good results when the waste material has an organic matter content of up to about 4%, it has been found that in the presence of higher percentages, the organic compounds present problems because they counteract the cement reaction, as a result of which an end product is formed which is less hard and from which the fixed material can be leached out more rapidly.
Moreover, it has been found that clay can be broken down during the cementation because the aluminum components of clay can dissolve as a result of the basic medium formed by the cement.
Another problem is to be ascribed to the fact that usually not only organic compounds are present in the waste material, but also inorganic compounds, such as, for example, heavy metals. Inorganic substances, are, however, not always bound by a clay. In order to overcome this, it is known to add an additive suitable for the relevant inorganic material, as a result of which the material is precipitated and thus can be incorporated in the cement matrix to be formed.
Because the end product formed behaves like a hardened concrete, it can, however, erode or disintegrate in the course of time. One problem which concrete is known to have is that it disintegrates in the course of time under the effect of frost/thaw. Care must then also be taken that frost/thaw cannot exert any influence, for example by covering the material with a layer of leaf mould. This also applies in the case of the concrete-like end product which is obtained as has been described above. This known end product can therefore also not be used in bridge piers and the like, but can only be dumped, or is used as foundation material.